Method of controlling the efficiency of blade hydromachines with considerable head variations

ABSTRACT

A method for controlling the efficiency of blade hydro machines having considerable water head variations at a hydro station consists in that provision is made for the arrangement of only a part of the blades on a runner whose parameters correspond to the maximum head during the period of its operation with the minimum head, said blades being arranged symmetrically about the hydro machine axis. Furtheron, as the head rises, more blades are provided on the runner, they all being also arranged symmetrically about the axis of the hydro machine.

United States Patent 1 1 Lesokhin et al.

[ METHOD OF CONTROLLING THE EFFICIENCY OF BLADE HYDROMACHINES WITH CONSIDERABLE HEAD VARIATIONS [76] Inventors: Jury Abramovich Lesokhin, ulitsa Lensoveta, 32, kv. 75; Anatoly Grigorievich Ivlev, Okhtinsky prospekt, 6/2, kv. 67, both of Leningrad, USSR.

22 Filed: Dec. 29, 1972 211 Appl. No.: 319,791

[30] Foreign Application Priority Data Jan. 12, 1972 U.S.S.R 1736683 [52] US. Cl 416/1, 416/244, 415/1, 415/195 [51] Int. Cl. F0ld 17/00 [58] Field of Search 415/119, 195, DIG. 3, 1; 416/244, 245, 1, 223

[56] References Cited UNITED STATES PATENTS 1,668,018 5/1928 Hollander 415/D1G. 3 UX 11 3,865,507 [451 Feb. 11,1975

3,543,368 12/1970 Marlow 415/D1G. 3 UX FOREIGN PATENTS OR APPLlCATlONS 1,260,071 3/1961 France 416/204 447,950 5/1936 Great Britain 416/168 876,981 9/1961 Great Britain 416/205 897,907 5/1962 Great Britain 415/D1G. 3

Primary Examiner-Everette A. Powell, Jr. Anorney, Agent, or Firm-Holman & Stern [57] ABSTRACT A method for controlling the efficiency of blade hydro machines having considerable water head variations at a hydro station consists in that provision is made for the arrangement of only a part of the blades on a runner whose parameters correspond to the maximum head during the period of its operation with the minimum head, said blades being arranged symmetrically about the hydro machine axis. Furtheron, as the head rises, more blades are provided on the runner, they all being also arranged symmetrically about the axis of the hydro machine.

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Pmmgnrtanma I SHEET 8 OF 8 Z a; 9 4h MN, MW W 9 W 0 METHOD OF CONTROLLING THE EFFICIENCY OF BLADE HYDROMACI-IINES WITH CONSIDERABLE HEAD VARIATIONS The present invention relates to the sphere of hydro machine-building and more particularly to the methods of controlling the efficiency of blade hydromachines having considerable head variations.

Such strain of blade hydromachines is most frequent, for example, in the initial (starting) period of their operation when the upper reservoir is not filled to capacity. The water head at a hydro station in this period is far lower than the minimum one to be reached in subsequent years and enabling the normal operation of blade hydro machines. When operated in the initial period, a blade hydro machine, e.g., a turbine, is characterized by an extremely low efficiency due to heavy hydraulic loss. With the water head being far lower than the minimum one, i.e., when the water possesses limited energy and imparts it to the runner, the number of r.p.m. of the runner shaft is supposed to be reduced. However, the present-day AC grids service regulations stipulate the maintenance of generated power at a constant frequency; therefore, the runner shaft r.p.m. must be kept constant. Keeping said r.p.m. constant in the starting period results in an unfavourable flowaround of the runner blades by a water stream, which increases hydraulic losses and leads to a marked drop in turbine efficiency. The unfavourable flow-around of the turbine blades brings about, in addition, the emergence of vortices disturbing to the stationary flow of the water stream in the flow-type portion of the turbine and causing a stepped-up cavitation erosion of the elements of said flow-type portion, and its runner blades, in particular, which leads to an increased vibration of the turbine runner, i.e., to its intense wear.

A method is known for increasing the efficiency of hydro station machines which run with considerable water head variations occurring due to either a limited capacity ofa reservoir or to the changing-over from the turbine mode to the pump operation, as is the case, for instance, with a reversible hydro machine (pumpturbine) at the Ananaigawa water storage station where water heads vary from 30 to 70 m.

In order to raise the efficiency of the high-head runner of the pump-turbine, its shaft is connected with a two-speed motor-generator designed to control the runner shaft r.p.m. so as to ensure that one of the two possible synchronous r.p.m. of the shaft due to variations in the number of pairs of working poles, in accordance with the known relation:

n 60'v/P,

where v is the frequency of AC generator or consumed by the motor-generator (in Hertz);

P is the number of pairs of working poles; and

n is the synchronous r.p.m.

When water heads at a hydro station are low, all the poles provided in the motor-generator are at work.

With said heads increasing substantially, some of the poles are engaged, the r.p.m. can be reduced in accordance with the above relation.

The two-speed motor-generator helps raise appreciably the efficiency of the pump-turbine runner despite considerable variations in the water head; its manufacture involves, however, large capital investments. The cost of the said two-speed motor-generator is well above that of the conventional-type one-speed motorgenerator, which raises the price of a hydro unit con- 0 sisting of a two-speed motor-generator and a pumpturbine. Such a method of increasing the efficiency of the hydro machine runner having considerable variations of the water head has not found wide application so far.

It is therefore an object of the present invention to raise the efficiency of the runner of the blade hydro machine intended for operation with a high water head or during the starting period, i.e., when the water head in the hydro station is lower than the minimum one.

Another object of the invention is to decrease the vibration intensity.

A further object of the invention is to decrease the cavitation erosion of the blade hydro machine.

According to the abovementioned and other objects of the invention, it suggests a method of controlling the efficiency of blade hydro machines having considerable variations in the water head, which according to the invention, provides for the use of a runner whose parameters are designed to meet the maximum water head; when the runner is operated with the minimum head, provision is made for the function of a part of the whole number of blades, the blades being arranged symmetrically about the axis of the hydro machine; the water head being on the rise, the number of blades should be increased and their position about said axis should be also symmetrical.

Such a method for controlling the efficiency of blade hydromachines helps to secure a considerable increase in the efficiency of the blade machine runner despite its running with considerable variations in the water head at a hydro station, e.g., during the starting period, there is a decrease in the intensity of the vibration and cavitation erosion. It is well-known that a water stream flows around easier when the blades of the hydro machine runner has a limited number of blades for the low water head. As a result of the better flow-around of the blades, the hydraulic loss of the energy required for the formation of a vortex becomes less and, consequently, the runner efficiency is higher; moreover, the stream flow in the flow-type portion of the runner becomes more steady, the cavitation erosion of the elements of the flow-type portion, the runner blades, in particular, decreases and the vibration of the machine runner is greatly reduced. This greatly helps improve the running of the machine, raises its dependability and extends its life.

Other peculiar features and advantages of the invention will be more apparent from the following exemplary embodiments of the method of controlling the ef ficiency of blade hydromachines with considerable water head variations at a hydro station and with reference to the drawings, wherein:

HO. 1 shows a graph of the universal characteristics of the Caplan turbine having an eight-blade runner designed to operate with a head close to m;

FIG. 2 shows schematically the adjustable blades of the Caplan turbine runner, arranged symmetrically about the hydro machine axis, when operated with a water head of less than 50 m;

FIG. 3 shows a graph of the universal characteristic of the same Caplan turbine runner operated with a water head equal to 24 m, according to the invention, the sleeve of the runner bears four adjustable blades;

FIG. 4 shows a graph of the comparative curves of efficeincy (17) variations depending on a given flow rate (Q") at a constant value of given runner r.p.m. (n,' 125) built on the base of the universal characteristics shown in FIGS. 1 and 3;

FIG. 5 shows a graph of the comparative curves of variations of the efficiency (1 depending on the given flow rate (Q at a constant value of the given runner r.p.m. (n;' 150) built on the base of the universal characteristics shown in FIGS. 1 and 3;

FIG'. 6 is a graph of the comparative curves of variations of the efficiency (1;) depending on the given flow rate (0 at a constant value of the given runner r.p.m. (m' 170) built on the base of universal characteristics shown in FIGS. 1 and 3;

FIG. 7 shows a graph of the universal characteristic of a diagonal turbine with a ten-blade runner designed to operate with heads close to 100 m;

FIG. 8 shows a graph of the universal characteristic of the same runner of the diagonal turbine, when operated with heads of less than 60 m, according to the invention;

FIG. 9 shows a graph of the comparative curves of variations of the efficiency (0) depending on a given power (N at a constant value ofa given runner r.p.m. (n, I 16) built on the base of the universal characteristics shown in FIGS. 7 and 8;

FIG. 10 shows a graph of the curves of variations of the efficiency (0) depending on a given power (N,) at a constant value of a given runner r.p.m. (n '=l27) built on the base of the universal characteristics shown in FIGS. 7 and 8;

FIG. 11 shows a graph of the comparative curves of variations of the efficiency (n) depending on a given power N,') at a constant value of a given runner r.p.m. (n,' 134) built on the base of the universal characteristics shown in FIGS. 7 and 8;

FIG. 12 shows a graph of variations of the efficiency (n) of the generator when its power (N) decreases, as compared with the nominal one adopted as 100 percent;

FIG. 13 shows schematically'a variant of the arrangement of three blades on the sleeve of a nine-blade runner symmetrically about the hydro machine axis; and

FIG. 14 shows another variant of the six blades arrangement on the sleeve of a nine-blade runner symmetrically about the hydro machine axis, their axial symmetry about the two-blade remaining intact.

The method of controlling the efficiency of blade hydro machines having considerable water head variations at the hydro station is considered herein below with, the Caplan turbine with an eight-blade runner and the diagonal turbine with a lO-blade runner taken as examples. The Caplan turbine is designed for operation in a hydro station having a water head close to 70 m. The universal characteristic (FIG. 1) of this turbine is a family of the curves having constant values for the efficiency (0) from 91 percent and lower in a coordinate plane of Q and in, where Q is a given flow rate and n is a given r.p.m.

The given flow rate is determined from the formula:

H is the water head at the hydro station; D, is the diameter of the runner, counted in meters along the peripheral tips of the blades. The given r.p.m. (m) is determined from the formula:

where n is the turbine runner r.p.m.

Included into the field of this universal characteristic are the curves having constant values for the angles of adjustment of the runner blades, these angles varying from 5 to d +20; the curves of constant openings (A of the turbine guide apparatus indicate variations in the openings over a range of from A, 20 mm to A 36 mm. The values of the openings (A of the guide apparatus of the turbine correspond to a turbine model with the diameter of the runner D being equal to 460 mm.

From FIG. 1 it is clear that the position of point A corresponding to the maximum efficiency of 91 percent is in correspondence with the given r.p.m. n, 100. Then, using the formula for n it is possible to determine the product n D for the water head being equal to m. The synchronous r.p.m. of the turbine rotor is given as n l66.7, and it is possible to determine the runner diameter which is equal to 5 m. In case of considerable variations in the waterhead, e.g., when it decreases to 24 m, the given r.p.m. (n,) of the Caplan turbine is determined as 170 from the formula determining the given r.p.m. n From the universal characteristic it appears that the maximum efficiency corresponding to the given r.p.m. of n, 170 is somewhat less than 79 percent, which means that the efficiency level decreased l2 to 14 percent.

In case the water head is, for example, H 24 m, only part of the total number of the same blades 2, four, specifically, are arranged on a sleeve 1 (FIG. 2) of the Caplan turbine runner, said blades 2 being positioned symmetrically about the hydro: machine axis (not shown in the figure).

The openings in the sleeve 1 that remained unclosed should be closed by flanges 3 ensuring the streamlined shape of said sleeve 1.

From the universal characteristic (FIG. 3) built for the four-blade runner, it is clear that the position of point A standing for the maximum efficiency of n 91% corresponds to the given r.p.m. of n 125. With preassigned values for the runner diameter D 5.0 m and the synchronous r.p.m. of the rotor n l66. 7, the value of the given r.p.m. n, corresponds to the water head H 45, which follows from the formula for m. Then it is necessary to find the efficiency value for the given r.p.m. m 125 from the universal characteristics (FIGS. 1 and 3) obtained for an eight-blade and a four-blade runner of the Caplan turbine and to build the graphs of the comparative curves of the efficiency variations (9) depending on the given flow rate Q, (FIGS. 4, 5, and 6).

The comparison of the curve of efficiency variations for the eight-blade runner of the Caplan turbine shown in FIG. 4 by a continuous line with the curve of efficiency variations for the four-blade runner, indicated by dash dot line in said figure, said runner being pro vided with the same set of blades on a sleeve as that of the eight-blade runner and the water head being one and the same, the H 45 m, i.e., with the value of the given r.p.m. being n, I25, shows that the maximum efficiency of the four-blade runner is 1 percent higher than that of the eight-blade runner. The advantage of the four-blade runner grows as the given flow rate decreases from the value of Q, I150 I/sec. For instance, when the value of the given flow rate is Q 400 I/sec, the four-blade runner efficiency is 3 percent higher than that of the eight-blader. With water heads lower than 45 m, the advantages of the four-blade runner are still more evident.

In comparison of the curves of the efficiency variations of the four-blade and eight-blade runners being considered depending on the given flow-rates (0,) with a water head H 31 m, i.e., with the given r.p.m. being n, 150 (FIG. 5), shows a marked advantage for the four-blade runner throughout the entire range of variations in the given flow rates. The maximum efficiency of the four-blade runner is 5 percent higher than that of the eight-blader.

The advantage of the four-blade runner as for its effi ciency is still greater when the water head is H 24 m. The curves of variations of the efficiency (6), shown in FIG. 6, depending on the given flow rates (0,) for the water head H 24 m, i.e., when the given r.p.m. values are n, I70, show that the maximum efficiency of the four-blade runner is 9 percent higher than that of the eight-blader.

The operation of a blade hydro machine designed to be used with a high water head during periods characterized by a notable decrease of the water head shows a marked increase in the machine efficiency, this made possible by the method of the invention.

Another example for application of the method of controlling the efficiency of blade hydro machines having considerable water head variations is a diagonal turbine with a IO-blade runner. This turbine is intended for a water head at a hydro station close to I00 m.

The universal characteristics of this turbine is shown in FIG. 7.

The values of the openings (Q of the guide apparatus of the turbine are in compliance with its modification having a runner diameter of D 425 mm. The value of this diameter is by counting the points crossing the axis of rotation of the blades from their peripheral end tips. From FIG. 7 it is clear that the position of point B indicating a maxim um efficiency of n 90 percent corresponds to the given r.p.m. of n, 90. Then it is possible to find the product n D using the formula given for n, for a water head of 100 m. Assuming ,the synchronous turbine rotor r.p.m. is n 150, the runner diameter (D of 6 m. is determined.

With considerable water head variations at a hydro station, specifically, when the head decreases to 40 m, the given r.p.m. (n,) of the diagonal turbine is 142.5 in accordance with the formula used to determine the given r.p.m. (11 From the universal characteristic it is clear that the maximum efficiency corresponding to the given r.p.m. of n, 142.5 is somewhat less than 80 percent, i.e., the said efficiency is decreased by about percent.

For a water head of, say, H 40 m, the sleeve of the same runner of the diagonal turbine bears only some of the blades, namely five blades. The blades are arranged symmetrically about the hydro machine axis by placing them through one nest in the sleeve, which is similar to the one shown in FIG. 2. The openings on the sleeve remaining open should be closed by flanges in order to ensure the streamlined shape of the said sleeve. It is clear from the universal characteristic (FIG. 8) built for the five-blade runner, that the position of point B indicating the position of the maximum efficiency of 0 percent corresponds to the given r.p.m. of n, I I6.

However, the maximum efficiency of the five-blade runner of the diagonal turbine is 5 percent lower than that of the initial lO-blade runner. In this particular case, the effect of changing from the ten-blade to the five-blade runner, expressed in the displacement of the point b (FIG. 7) of the maximum efficiency toward a higher given r.p.m., i.e., toward lower water heads, is somewhat decreased by a sharp fall in the value of this efficiency. In order to raise the efficiency of the fiveblade runner is the course of its operation characterized by low heads, it is expedient that the five blades provided for the given period have a shape corresponding to the shape of the low-head water stream, i.e., that differ in form from the initial ten blades.

An increase in the maximum efficiency as compared with the one obtained at point B of FIG. 8 which is equal to n 85 percent can be predicated as 2 percent. This is the minimum value that can be expected with the properly designed runner. A further comparison of the efficiencies of the two runners whose universal characteristics are shown in FIGS. 7 and 8 is based on another case when the five-blade runner has blades specially designed for the lower water heads.

With the values of the runner diameter and the rotor synchronous r.p.m. preset at D, 6.0 m and n respectively, the given r.p.m. r1 I 16 corresponds to the water head H 60 m., which stems from the formula for n,'. Furtheron, the efficiency (6) is determined for the obtained r.p.m. of n, 116 using the universal characteristics (FIGS. 7 and 8) for the 10- blade and five-blade runners of the diagonal turbine and a graph is built for the comparative curves of variations of the efficiency (0) depending on the given power N, (FIG. 9) for the lO-blade runner and the five-blade runner fitted with blades similar to those in the ten-blader and with the specially designed ones for lower heads. The value of the given power is determined from the universal characteristic using the formula:

Comparison of the curves shows that the ten-blade runner (its characteristic is shown by a continuous line) at a water head of 60 m excels by its maximum efficiency, the five-blade runner fitted with similar blades (its characteristic is shown by a dot dash line) and is somewhat inferior to the five-blade runner with the specially designed blades (its characteristic is shown by a dot line), especially at values N exceeding 9 kwt. However, with the lower water heads, the five-blade runners offer considerable advantages that tend to increase as the water head decreases. With a water head of 50 m, i.e., when the given r.p.m. is n, 127, the efficiency levels of the ten-blade and the five-blade runners fitted with blades having similar shape coincide, while the five-blade runner with the specially designed blades is superior to the above runners for that-index by some 2 percent (FIG. 10).

FIG. 11 shows the curves characterising the efficiency variations depending on the given power N, for the very same three runners having an H 45 m, i.e., when n, 134 r.p.m. with such a water head, the fiveblade runner fitted with the same blades as those in the lO-blader excels the latter as to the maximum efficiency by some 1.5 and by 3.5 percent in case of the grater power of N 10.5 kwt. The efficiency of the five-blade runner with the specially designed blades is 3.5 percent higher than that of the ten-blader runner at the point of maximum efficiency and is 5.5 percent higher when N, 10.5 kwt.

Such favourable characteristics for the five-blade runners at the high power values secures a considerable increase in the power being generated. By comparing the point a corresponding to the maximum efficiency of the ten-blade runner with the point b on a similar curve relating to the five-blade runner with blades being similar in shape to those on the ten-blade runner, it is possible to see that, with the efficiency being of same value, the IO-bIade runner permits an increase of electricity output by 27 percent, as N, increases from 8.25 kwt for the ten-blade runner to 10.5 kwt for the five-blade runner.

Such a marked power increase produces a favourable effect on the working conditions of the generator.

A notable decrease in the water head results in a drop in generated power; therefore, the working point of the turbine is displaced from point (FIG. 12) correspond ing to the turbine operation having a full head of H 100 m to a point a corresponding to the head of 45 m. This displacement of the working point c of the turbine to point a is followed by a drop in the generator efficiency by some 4 percent. The increase in the power involved in the changing-over from the ten-blade runner to the five-blade results, according to the invention, in a rise in the generator efficiency of 1 percent (transition from point a to point b).

Thus, the effect of the proposed method not only involves an increase of both the turbine efficiency and generated power but also raises the generator efficiency.

Some of the likely variants for the arrangement of part of the blades of a runner whose parameters correspond to the maximum water head and which is operated with a minimum head are shown in FIGS. 13 and 14, said arrangement for part of the blades being symmetrical about the hydro machine axis.

The runner shown in FIG. 13 is a nine-blade runner which is operated, for example, during its starting period, with three blades 2 arranged in openings in a sleeve 1. The openings for the remaining blades are closed by flanges 3. Such an arrangement for the blades is expedient in case of considerable head variations in different periods of the hydro station operation. By unfolding the blades 2 of the runner by to 15 toward closing, it is possible to raise the efficiency of the threeblade runner.

If the range of water head variations is not so wide, provision is made in the same sleeve 1 (FIG. 14) for fixing six blades 2. For the main period of operation with high water heads a runner fitted with nine blades is used and, consequently, there are nine openings in its hub. Only three blades can be uniformly arranged around the hub when the number of blades is decreased from nine. During the turbine operational period when the water head is a fraction of the rated one, nine blades may prove to be too many while three blades may prove to be too few. In this case, six blades may be used. as shown in FIG. 14. The gain will be somewhat less than in the case of applying a new runner with a new hub bearing six openings uniformly arranged around the hub for the blades to be secured therein. However, by arranging the blades, as shown in FIG. 14, it is possible to obtain at least a partial effect without manufacturing any novel parts and performing any complicated procedures.

Axial symmetry can be also maintained about groups of three and more blades each, however, on the condition that the center of gravity of the runner should coincide with its axis of rotation. The method of controlling the efficiency of blade hydromachines having considerable head variations, according to the invention, is easy to be realized and gains great economic effect during the starting period when the hydro machines are being run with low water heads. This effect is summed up of: first, power generated additionally by the turbine both at the expense of a higher efficiency and as a result of the possibility that an earlier opening of the starting period of their operation before high water sets in the upper reservoir at the hydro station, i.e., with a head lower than that permissible so far;

secondly, that of reduced intensity of vibration and cavitation erosion, which helps to increase the dependability of the hydro machines and extend the duration of their operation in between repairs.

What we claim is:

l. A method of controlling the efficiency of a blade hydro machine having considerable water head variations at a hydro station, comprising: arranging on a runner whose parameters correspond to the maximum water head only some of the blades during its operation with a minimum head: arranging said blades symmetrically about the axis of said hydro machine; and increas-' ing the number of the said blades as the head rises, said blades being also arranged symmetrically about the axis of said hydro machine.

2. The method according to claim 1, wherein four blades are arranged at the minimum head and eight blades are arranged at the maximum water head.

3. The method according to claim 1, wherein three blades are arranged at minimum head and nine blades are arranged at maximum water head.

4. The method according to claim 1, wherein five blades are arranged at minimum head and 10 blades are arranged at maximum water head.

5. The method according to claim 1, further comprising providing the blades at minimum head with a shape corresponding to the shape of a low water head. 

1. A method of controlling the efficiency of a blade hydro machine having considerable water head variations at a hydro station, comprising: arranging on a runner whose parameters correspond to the maximum water head only some of the blades during its operation with a minimum head: arranging said blades symmetrically about the axis of said hydro machine; and increasing the number of the said blades as the head rises, said blades being also arranged symmetrically about the axis of said hydro machine.
 2. The method according to claim 1, wherein four blades are arranged at the minimum head and eight blades are arranged at the maximum water head.
 3. The method according to claim 1, wherein three blades are arranged at minimum head and nine blades are arranged at maximum water head.
 4. The method according to claim 1, wherein five blades are arranged at minimum head and 10 blades are arranged at maximum water head.
 5. The method according to claim 1, further comprising providing the blades at minimum head with a shape corresponding to the shape of a low water head. 